The FBI has joined the effort and police have set up road checks to question drivers who may have seen anything that could be a clue.

"I just know God is looking after her," Jo Ann Cornwell told "Good Morning America" Monday of her daughter. "And she has great faith in God. And that's where I'm putting my strength."

Mike Ayers, an agent with the Georgia Bureau of Investigation, told WSB that the FBI would bring in a behavioral scientist and assist with cell phone information.

Cornwell, mother to a son, Brody, now 15, was on her cell phone with boyfriend Douglas Davis as she was out for a stroll around 9 p.m.

Davis told police that Cornwell said a car was approaching her. He then heard a struggle and Cornwell yelled, "Don't take me".

Then Davis lost reception.

Jo Ann Cornwell said Davis' next call was to her to tell what he had heard. Horrified, she then called 911.

"It terrified me," she said, her voice cracking. "I couldn't believe what he was saying."

Cornwell's brother, Richard Cornwell, told "Good Morning America" that investigators with the Georgia Bureau of Investigation are still unsure whether his sister's abduction was random or if she was targeted, possibly in relation to her job as a former probation officer.

"Her son needs his mother back, and I need my baby back," Jo Ann Cornwell said, crying. "And we believe we're going to get her back."

Cornwell's cell phone was found Friday evening, according to police. A man was mowing his lawn when he found the phone, more than three miles from where investigators believe Cornwell was kidnapped.

Richard Cornwell said that single piece of evidence has given the family the most hope that Cornwell would be brought home.

Found along a major thoroughfare, not the back street from where Cornwell disappeared, the phone indicates the kidnappers' route, Richard Cornwell said.

"That's very encouraging to me, because we know the direction of travel," he said. "We know they were heading north on State Route 325."

From there, he said, they could have driven into Tennessee or North Carolina. Or, he said, just doubled back into Georgia.

"That gives me hope that there is still a good chance she's out there somewhere," he said.

Police, however, have told ABC News that they may soon be forced to scale back their search.

Police Believe Kristi Cornwell Is in Danger

At the scene of the kidnapping, police have also discovered signs of a struggle and some of Cornwell's belongings along Jones Creek Road, a rural road in north Georgia.

"The belief is it was a kidnapping, and she is in danger," said John Bankhead, spokesman for the Georgia Bureau of Investigation.

The Georgia Bureau of Investigation believes Cornwell was abducted by vehicle and is now searching for a white SUV and a tan or gold subcompact car, possibly a Toyota or Nissan, that were seen in the area on the evening of Aug. 11.

For nearly a week, 100 people from more than 15 agencies have been searching for Cornwell.

Richard Cornwell said that his sister's boyfriend was not considered a suspect or a person of interest in the case.

Last year, another woman, Meredith Emerson, disappeared in the same area of northern Georgia. She was found murdered and her killer was caught and put behind bars.

But the people combing the countryside for Cornwell can't believe this is happening again. "We're in a rural community, you wouldn't think it would be like this," one man who lives in the area said.

Friends and family started a "Pray for Kristi Cody Cornwell" group on Facebook. There are more than 3,000 members so far.

One message read, "We love you and Brody and are praying for your safe return."

Cornwell was very active in her community and her church, taking part in a mission to Jamaica with her son Brody.

Anyone with information can call the Union County Sheriff's office at (706) 439-6038, or the Georgia Bureau of Investigation at (800) 597-8477.

CLICK HERE for more information about Kristi Cornwell and the reward for information leading to her whereabouts.